Illumination device

ABSTRACT

An illumination device includes a light source; a secondary light source forming system for forming predetermined secondary light sources by use of light from the light source, the secondary light source forming system including a plurality of lens array units disposed in the direction of an optical axis and each having a plurality of lens elements distributed in a plane perpendicular to the optical axis; an optical system for directing light from the secondary light sources to a surface to be illuminated; and an actuating device for displacing at least one lens array unit in the direction of the optical axis to adjust the illuminance distribution on the surface being illuminated, while maintaining a substantially constant range of illumination on the surface being illuminated.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to an illumination device and, more particularly,to an illumination device for adjusting or controlling an illuminancedistribution on a surface, such as a surface of a mask, for example, tobe illuminated.

When, in a semiconductor device manufacturing exposure apparatus, thereis a non-uniform the illuminance distribution on the surface of a mask(which is a surface to be illuminated), there occurs unevenness in thelinewidth of a pattern transferred onto the surface of a wafer. Becauseof the recent demand for the manufacture of extraordinarily finepatterns (IC patterns), the precision of uniformness in the linewidthshould be increased. For example, the precision should be not greaterthan ±1% which is remarkably lower than the traditionally requiredprecision (±3%).

Also, in accordance with the requirements of miniaturization, higherprecision is required also with regard to the illuminance distributionon the surface of a mask. Namely, highly uniform distribution or exactlydesired distribution should be provided.

In order to meet these requirements, there have been proposedillumination devices for adjusting the illuminance distribution on thesurface to be illuminated, such as a mask surface, as disclosed inJapanese Laid-Open Patent Applications, Laid-Open Nos. Sho61-267722 andSho62-52929, both filed in Japan in the name of the assignee of thesubject application.

According to the proposed illumination devices, it is possible toprovide a quite uniform or exactly desired illuminance distribution onthe surface being illuminated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedillumination device for adjusting or controlling the illuminancedistribution.

Briefly, in accordance with one aspect of the present invention, thereis provided an illumination device which includes a light source;secondary light source forming means for forming predetermined secondarylight sources by use of light from the light source, the secondary lightsource forming means including a plurality of lens array units disposedin the direction of an optical axis and each having a plurality of lenselements distributed in a plane perpendicular to the optical axis; anoptical system for directing light from the secondary light sources to asurface to be illuminated; and actuating means for displacing at leastone lens array unit in the direction of the optical axis to adjust theilluminance distribution on the surface being illuminated, whilemaintaining a substantially constant range of illumination on thesurface being illuminated. With this arrangement, the light can beefficiently directed to the surface to be illuminated, and the surfacecan be illuminated with a desired illuminance distribution.

Preferably, the plural lens array units comprise, in an order from thelight source side, a first lens array unit having a positive refractingpower, a second lens array unit having a negative refracting power and athird lens array unit having a positive refracting power. For example,the second lens array unit is displaced to change spherical aberrationto be caused by the secondary light source forming means and, by doingso, the illuminance distribution on the surface being illuminated can beadjusted.

Significant advantageous effects are attainable when the illuminationdevice of the present invention is incorporated into an exposureapparatus for transferring a pattern of a mask onto a wafer. Namely,when this is done, it is possible to remarkably improve the patterntransfer characteristics of the exposure apparatus.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic and diagrammatic view of an illumination deviceaccording to one embodiment of the present invention.

FIG. 1B is a schematic and diagrammatic view showing details of theoptical arrangement of a optical system included in the embodiment ofFIG. 1A.

FIGS. 2A and 2B are schematic views, respectively, for explicating themanner of adjustment of the illuminance distribution.

FIGS. 3A-3C each shows the relationship between the illuminancedistribution and spherical aberration caused at a spherical aberrationcreating portion.

FIG. 4 is a schematic and diagrammatic view of an illumination deviceaccording to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a schematic block diagram of one embodiment of the presentinvention, and FIG. 1B is a schematic view showing a specific example ofan optical system usable in the FIG. 1A embodiment. In these Figures,denoted at 1 is a light source which comprises, for example, a superhigh pressure Hg lamp. Denoted at 2 is a condensing means whichcomprises an elliptical mirror, for example. The light source 1 isdisposed in the neighborhood of a first focal point of the ellipticalmirror 2. Denoted at 3 is an aberration controlling means which includesan aberration producing portion 4 and an actuator (drive) 5. Theaberration producing portion 4 functions to produce spherical aberrationby use of an optical system that constitutes the aberration controllingmeans 3, and also functions to emit a light. The actuating portion 5functions to displace one or more members, such as lenses, which areconstituent elements of the spherical aberration producing portion 4, tothereby change the spherical aberration caused by the aberrationproducing portion 4.

In the present embodiment, the spherical aberration producing portion 4comprises an optical integrator which includes three lens array units4-1, 4-2 and 4-3 each having a plurality of minute lenses arrayedone-dimensionally or two-dimensionally in a plane orthogonal to theoptical axis of the illumination device. The optical integrator 4 has alight entrance surface 4a which is disposed in the neighborhood of asecond focal point of the elliptical mirror 2. Also, the opticalintegrator 4 has a light exit surface 4b which provides a secondarylight source surface that comprises a number of secondary light sources.The light exit surface 4b of the optical integrator is located at aposition at which parallel light, having been projected on the lightentrance surface 4a is converges.

Denoted at 6 is a light projection means which comprises a condenserlens, for example. The projection means 6 functions to illuminate, byuse of a multi-beam light from the light exit surface 4b of the opticalintegrator 4, a surface 7 to be illuminated, with respect to whichsurface the surface of a mask or reticle should be positioned. Denotedat 8 is an illuminance measuring device having a sensor device (notshown) such as a two-dimensional image pickup device, a movableone-dimensional sensor array or a movable photodetector, for measuringthe illuminance distribution on the surface 7 being illuminated, on thebasis of output signals of the sensor means. The measured value or aninstruction signal corresponding to that value is supplied to theactuating portion 5. Denoted at 9 is an output device for outputting, asrequired, the measured value supplied from the illuminance measuringdevice 8.

In the present embodiment, the light from the light source 1 is directedand projected, by use of the elliptical mirror 2, to and on the opticalintegrator 4 which is positioned so that its light entrance surface 4ais positioned in the neighborhood of the second focal point of theelliptical mirror 2. The light fluxes emanating from the minute lenses(secondary light sources) constituting the light emitting surface 4b ofthe optical integrator 4 are projected and superposed upon one anotheron the surface 7 by means of the condensers lens 6 which is fixed at apredetermined position.

Also, in the present embodiment, the surface 7 to be illuminated ispositioned in a focal plane, on an image side, of the condenser lens 6.Further, the surface 7 and the light entrance surface 4a of the opticalintegrator 4 are set to be held in an optically conjugate relationship.

The light emitting surface 4b of the optical integrator 4, namely, thesecondary light source surface, is positioned in another focal plane ofthe condenser lens 6 on the object side (light source side). Thus, forexample, the light flux emanating from the center of the secondary lightsource surface (i.e., the point of intersection of the secondary lightsource surface with the optical axis) is transformed by the condenserlens 6 into parallel light consisting of light rays advancing inparallel to the optical axis.

In the present embodiment, the optical integrator 4 is provided by threelens array units 4-1, 4-2 and 4-3, as illustrated in FIG. 1B, having, inthe order from the light source 1 side, positive, negative and positiverefracting powers. Of these lens array units, the lens array units 4-2is made displaceable by the actuating portion 5 in the direction of theoptical axis as shown by a double-headed arrow in FIG. 1B, to therebychange the spherical aberration, to be caused by the optical integrator4, with respect to the light incident on the optical integrator 4, whilesubstantially fixedly retaining the position of the secondary lightsource surface. By this structure, the conditions concerning theincidence of each light beam from the optical integrator 4 upon thecondenser lens 6 are changed to thereby adjust the illuminancedistribution to be defined on the surface 7. Also, by such adjustment,it becomes possible to make the illuminance distribution uniform. Forexample, any change in the illuminance distribution on the surface 7caused by the movement of the lens unit 4-2 may be detected on the basisof the output signals from the illuminance measuring device 8 and themovement of the lens array unit 4-2 may be controlled by the actuatingportion 5 so as to make the illuminance distribution uniform.

Next, a description will be provided of the principle of changing theilluminance distribution on the surface 7 by displacing the lens arrayunit 4-2.

FIGS. 2A and 2B are schematic views, respectively, each showing one setof lens elements each being a constituent element of a corresponding oneof the lens array units 4-1, 4-2 and 4-3 of the optical integrator 4,these lens elements in the one set being arrayed in a direction parallelto the optical axis. The manner of adjusting the illuminancedistribution will be explained with reference to these figures.

In FIGS. 2A and 2B, reference numerals 21, 22 and 23 denote minutelenses which are constituent members of the lens array units 4-1, 4-2and 4-3 of the optical integrator 4, respectively. As illustrated inthese figures, the lens 21 comprises a positive lens; the lens 22comprises a negative meniscus lens having a concave surface facing tothe light source side; and the lens 23 comprises a positive lens.Denoted at d is the spacing between the lenses 21 and 22, and denoted at1 is the spacing between the lenses 21 and 23.

The situation shown in FIG. 2B is such that, in the arrangement shown inFIG. 2A, the lens 22 has been displaced to the condenser lens 6 side soas to change the spherical aberration to be produced by the illustratedoptical arrangement.

Also, in the present embodiment, in order to assure that the refractingpower (focal length) of the optical integrator is always maintainedsubstantially constant, the minute lens 21 is displaced in the directionof the optical axis by a predetermined amount, with the displacement ofthe minute lens 22 in the direction of the optical axis and, also, inassociation with the direction and amount of the displacement of theminute lens 22. By doing so, it becomes possible to change theilluminance distribution while maintaining a substantially constantrange of illumination on the surface 7. In the illustrated example, thelens 23 is held fixed.

By moving the lens 22 toward the condenser lens 6 side, from the stateshown in FIG. 2A to the state shown in FIG. 2B, the positionalrelationship among the lenses 21-23 is changed to thereby change theheight and angle of incidence of light upon the lens 22. As a result ofthis, there occurs a change in the spherical aberration caused by theoptical system that comprises the lenses 21-23.

More specifically, when parallel light is projected upon the opticalintegrator 4, parallel light is projected through the condenser lens 6upon the surface 7, which is an optically conjugate plane with respectto the light entrance surface 4a, provided that no spherical aberrationis caused by the optical integrator. Namely, the position of incidenceof light upon the surface 7 is determined by the spherical aberration ofthe optical integrator 4. Therefore, by changing the sphericalaberration to be caused by the optical integrator 4, it is possible tochange the state of incidence of light upon the surface 7 and, as aresult of which, to change the illuminance distribution on the surface7.

As will be understood from the foregoing, in the present embodiment itis also possible to make uniform the illuminance distribution on thesurface 7 by changing the spherical aberration to be caused by theoptical integrator 4.

FIGS. 3A-3C are views explicating the relationship between theilluminance distribution on the surface 7 and the spherical aberrationcaused by the optical integrator 4, in the case where the lenses 21 and22 are displaced as has been described with reference to FIGS. 2A and2B. FIG. 3B corresponds to a case where the minute lens 22 is displacedby a suitable amount to produce a predetermined spherical aberration tothereby make the illuminance distribution substantially uniform. FIG. 3Acorresponds to the case wherein, because of the large amount of movementof the minute lens 22, the correction of the spherical aberration isinsufficient and, as a result the illuminance is too high, at themarginal regions of the surface 7. FIG. 3C corresponds to a case where,contrary to the FIG. 3A case, because of the small amount of movement ofthe minute lens 22, the correction of the spherical aberration isexcessive, such that the illuminance distribution on the surface 7 istoo high at the marginal regions.

FIG. 4 is a schematic diagram showing another embodiment of the presentinvention. The illustrated embodiment is an example where anillumination device is incorporated into a projection exposure apparatuswhich is called a "stepper". The same reference numerals are assigned tothose elements corresponding to or similar to the elements shown in FIG.1B.

The present embodiment differs from the FIG. 1B embodiment in that acircuit pattern (IC pattern) formed on the surface of a reticle,disposed on the surface 7 to be illuminated, is projected through areduction projection lens 10 upon the surface of a wafer 11 held on awafer stage 12.

In the present embodiment, a secondary light source surface formed by anoptical integrator which is a constituent element of a sphericalaberration producing portion 4 is placed in an optically conjugaterelationship with an entrance pupil of the projection lens system 10.This optically conjugate relationship is maintained irrespective ofdisplacement of one or more lens units of the optical integrator made tochange the spherical aberration. Further, the refracting power of theoptical integrator is maintained substantially fixed, as in theforegoing embodiment. Therefore, the range of illumination does notchange as a result of the adjustment of the illuminance distribution.Thus, the circuit pattern on the reticle surface can be illuminatedcorrectly and efficiently and, therefore, the circuit pattern can betransferred onto the wafer correctly.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An illumination device, comprising:a lightsource; secondary light source forming means for forming predeterminedsecondary light sources by use of light from said light source, saidsecondary light source forming means including a plurality of lens arrayunits arrayed in a direction of an optical axis, each lens array unithaving a plurality of lens elements disposed along a plane orthogonal tothe optical axis; an optical arrangement for directing light beams fromsaid secondary light sources to a surface to be illuminated, and forsuperposing the light beams one upon another on the surface to beilluminated; and means for changing the positional relationship of saidlens array units, in the direction of the optical axis, whilemaintaining a substantially constant refracting power of said secondarylight source forming means, to thereby adjust the illuminancedistribution on the surface to be illuminated.
 2. A device according toclaim 1, wherein said plural lens array units comprise, in an order fromthe light source side, a first lens array unit having a positiverefracting power, a second lens array unit having a negative refractingpower and a third lens array unit having a positive refracting power,and wherein said first and second lens array units are displaceablethrough said positional relationship changing means.
 3. A deviceaccording to claim 2, wherein said third lens array unit is immovablyfixed with respect to the direction of the optical axis.
 4. A deviceaccording to claim 3, further comprising a condensing optical system forconcentrating the light from said light source onto said first lensarray unit.
 5. An illumination device, comprising:a light source forproviding light of a predetermined wavelength; an optical integratorhaving a predetermined refracting power and a predetermined sphericalaberration with respect to said predetermined wavelength, for receivingthe light from said light source and for providing a plurality of lightbeams; means for directing the light beams from said optical integratorto a surface to be illuminated so that the light beams are superposedupon one another on the surface to be illuminated; and adjusting meansfor adjusting said predetermined spherical aberration of said opticalintegrator while substantially maintaining said predetermined refractingpower of said optical integrator, to change the illuminance distributionon the surface to be illuminated.
 6. A device according to claim 5,wherein said optical integrator includes first and second movable lensarray units disposed along an optical axis, each unit including aplurality of lens elements disposed along a plane perpendicular to theoptical axis, and wherein said adjusting means includes an actuator fordisplacing said first and second lens array units to change theilluminance distribution on the surface to be illuminated.
 7. A deviceaccording to claim 6, wherein the displacement of said first lens arrayunit by said actuator contributes to adjustment of said predeterminedspherical aberration of said optical integrator and the displacement ofsaid second lens array unit by said actuator contributes to compensatingfor a change in said predetermined refracting power of said opticalintegrator due to the displacement of said first lens array unit.
 8. Adevice according to claim 6, wherein said optical integrator furtherincludes a third lens array unit having a plurality of lens elementsdisposed along a plane perpendicular to the optical axis, and whereinsaid third lens array unit receives light that has passed through saidfirst and second lens array units to supply the light beams to saiddirecting means.
 9. An exposure apparatus for exposing a semiconductorwafer to a circuit pattern of a mask with light, said apparatuscomprising:a light source; secondary light source forming means forforming predetermined secondary light sources by use of light from saidlight source, said secondary light source forming means including aplurality of lens array units disposed along an optical axis, each lensarray unit having a plurality of lens elements disposed along a planeorthogonal to the optical axis; an optical arrangement for directinglight beams from said secondary light sources to the mask and forsuperposing the light beams upon one another on the mask; and means forchanging the positional relationship of said lens array units, in thedirection of the optical axis, while maintaining a substantiallyconstant refracting power of said secondary light source forming means,to thereby adjust the illuminance distribution on the mask.
 10. Anexposure apparatus for exposing a semiconductor wafer to a circuitpattern of a mask with light, said apparatus comprising:a light sourcefor providing light of a predetermined wavelength; an optical integratorhaving a predetermined refracting power and a predetermined sphericalaberration with respect to said predetermined wavelength, for receivingthe light from said light source and for providing a plurality of lightbeams; means for directing the light beams from said optical integratorto the mask so that the light beams are superposed upon one another onthe mask; and adjusting means for adjusting said predetermined sphericalaberration of said optical integrator while substantially maintainingsaid predetermined refracting power of said optical integrator, tochange the illuminance distribution on the mask to be illuminated.
 11. Adevice according to claim 10, said optical integrator includes first andsecond moveable lens array units disposed along an optical axis, eachunit including a plurality of lens elements disposed along a planeperpendicular to the optical axis, and wherein said adjusting meansincludes an actuator for displacing said first and second lens arrayunits to change the illuminance distribution on the mask to beilluminated.
 12. A device according to claim 11, wherein thedisplacement of said first lens array unit by said actuator contributesto adjustment of said predetermined spherical aberration of said opticalintegrator and the displacement of said second lens array unit by saidactuator contributes to compensating for a change in said predeterminedrefracting power of said optical integrator due to the displacement ofsaid first lens array unit.
 13. A device according to claim 11, whereinsaid optical integrator further includes a third lens array unit havinga plurality of lens elements disposed along a plane perpendicular to theoptical, axis, and wherein said third lens array unit receives lightthat has passed through said first and second lens array units to supplythe light beams to said directing means.